I came across this one Debian Linux installation (6.0.6), and examining its /etc/rsyslog.conf, I see configuration lines like this:
auth,authpriv.* /var/log/auth.log *.*;auth,authpriv.none -/var/log/syslog
I can't find anything about prepending dashes to the file action in rsyslog.conf(5), and what the meaning of it might be, and would like to know what they actually do.